In natural mineral oil deposits, mineral oil is often present in the cavities of porous reservoir rocks which are sealed toward the surface of the earth by impervious overlying strata. The cavities may be very fine cavities, capillaries or pores. Fine pore necks may, for example, have a diameter of only approximately 1 μm. As well as mineral oil and proportions of natural gas, the deposits often also comprise salt-containing water. More particularly, the use of assistants for mineral oil production from salt-rich rock formations may be difficult.
In mineral oil production, a distinction is made between primary, secondary and tertiary production. In primary production, the mineral oil flows, after commencement of drilling of the deposit, of its own accord through the borehole to the surface due to the autogenous pressure of the deposit. The autogenous pressure results from the load on the essentially water-filled overlying rock strata. However, the autogenous deposit pressure often declines rapidly in the course of withdrawal of mineral oil, and so it is usually possible to produce only approx. 5 to 10% of the amount of mineral oil present in the deposit by means of primary production, according to the deposit. Thereafter, the autogenous pressure is no longer sufficient for production of mineral oil, and so pumps are often used thereafter for further mineral oil production.
After primary production, secondary production can therefore be used, in which, in addition to the boreholes which serve for production of the mineral oil, called the production wells, further boreholes are drilled into the mineral oil-bearing formation. These are called injection wells and are used to inject water into the deposit (called “water flooding”), in order to maintain the pressure or increase it again.
As a result of the injection of water or of a corresponding aqueous formulation, the mineral oil is also forced gradually through the cavities in the formation, preceding from the injection well in the direction of the production well. However, this only works for as long as the relatively high-viscosity oil is pushed onward by the water. As soon as the mobile water breaks through to the production wells along preferred flow paths, it flows on the path of least resistance from this time, i.e. particularly through the flow paths formed, and barely displaces any oil. By means of primary and secondary production, generally only approx. 30 to 35% of the amount of mineral oil present in the deposit can be produced.
After the measures of secondary mineral oil production (or after measures of primary mineral oil production), measures for tertiary mineral oil production (also known as “enhanced oil recovery”, EOR) are also used to further enhance the oil yield. These include processes in which suitable chemicals, such as surfactants and/or polymers, are used as assistants in formulations for oil production. An overview of tertiary oil production using chemicals can be found, for example, in an article by D. G. Kessel from 1989 (Journal of Petroleum Science and Engineering, 2 (1989), 81 to 101).
One of the known techniques for tertiary mineral oil production is that known as “polymer flooding”, in which an aqueous solution of a thickening polymer is injected into the mineral oil deposit through the injection wells, the viscosity of the aqueous polymer solution being matched to the viscosity of the mineral oil. Instead of a polymer solution, it is also possible to use aqueous solutions comprising nonpolymeric thickeners.
Thickeners are chemicals which increase the viscosity of aqueous solutions, extending as far as gel formation. The injection of a thickened solution forces the mineral oil through the cavities in the formation preceding from the injection well in the direction of the production well, and allows the mineral oil to be produced through the production well. The fact that a thickener formulation has about the same mobility as the mineral oil reduces the risk that the formulation breaks through to the production well without having any effect (“fingering”).
Thus, it is possible with thickener to mobilize the mineral oil much more homogeneously and efficiently than in the case of use of mobile water, by avoiding the occurrence of “fingering” in the case of use of water. Furthermore, piston-like displacement of the oil is achieved by the matching of the mobility. This accelerates the production of the mobile oil with regard to water flooding.
In addition, in the case of tertiary mineral oil production, it is also possible to use surfactants in addition to thickeners. Surfactants are used in mineral oil production in order to lower the oil-water interfacial tension to very low values and thus to mobilize further mineral oil which would otherwise remain in the rock.
The subsequent injection of a thickened water solution forces the mineral oil thus mobilized, as in the case of water flooding, preceding from the injection well in the direction of the production well, thus allowing it to be produced through the production well. Details of flooding with thickened or surfactant-containing solutions and components suitable therefor are described, for example, in “Petroleum, Enhanced Oil Recovery” (Kirk-Othmer, Encyclopedia of Chemical Technology, John Wiley & Sons, 2005).
In some cases, such a combination of successive “surfactant flooding” and “polymer flooding” is preceded by a phase involving an alkaline agent such as sodium hydroxide solution, in order to mobilize natural surfactants present in the crude oil (“alkaline polymer-surfactant flooding”). For the aforementioned combination of successive “surfactant flooding” and “polymer flooding”, it is also possible to use what are called viscoelastic surfactants. These viscoelastic surfactants are interface-active substances which, in solution, form associates which increase the viscosity of the solution.
For examples thereof, reference is made to “Molecular Gels: Materials with Self-Assembled Fibrillar Networks” (Richard G. Weiss, Pierre Terech, Dec. 22, 2005), Advances in Colliod and Interface Science 128-130 (2006) 77-102). With viscoelastic surfactants, it is possible to achieve a reduction in interfacial tension which cannot be achieved with polymeric components alone. Thickening surfactants for mineral oil production are described in various places. “Oilfield Reviews” (Vol. 16(4) (2004) 10-28) describes the use of viscoelastic surfactant systems as “fracturing fluids”. As early as 1985, V. Shvets described the stabilization of suspensions by the use of nonionic surfactants (Journal of Applied Chemistry of USSR, 58 (6), 1985, 1220-1224).
The so-called associates that surfactants can form are also called micelles and form due to hydrophobic interactions.
The thickening properties of such solutions can generally be eliminated by shear, in which case the associates fall apart into smaller fragments. This operation, however, does not break any chemical bonds, and the associates develop their full thickening action again in the absence of shear.
This is an advantage of viscoelastic surfactant systems, more particularly over synthetic polymeric thickeners, which can be destroyed irreversibly by strong shear, for example in the course of pumping of a solution into an oil reservoir. An additional effect is the fact that viscoelastic surfactants lower the water-oil interfacial tension, which is the case only to a distinctly lesser degree, if at all, for polymers.
However, in order to develop viscoelastic surfactant systems that can economically be used on a large scale for enhanced oil recovery, it is necessary to develop a short route to tris(2-hydroxyphenyl)methane derivatives that is both economical and non-toxic.
G. Casiraghi et al. [Tetrahedron Letters, No. 9, 679-682 (1973)] describe the synthesis of tris(2-hydroxyphenyl)methane derivatives by reacting alkylphenoxy magnesium halides with triethylorthoformiate. The reaction is effected by deprotonation of the phenol derivatives with a Grignard reagent and subsequent addition of triethylorthoformiate to afford tris-phenoxides. This reaction is also described in Dinger et al. [Eur. J. Org. Chem. 2000, 2467 2478].
The main disadvantages ensuing from synthesizing tris(2-hydroxyphenyl)methane derivatives by using Grignard reagents are the general hazardousness of these reagents and the large amounts of different solvents that have to be used in order to keep the Grignard reagents in solution.
Another disadvantage of this protocol is the evolution of flammable ethane gas upon generation of the magnesium salt by treatment of the phenol derivative with EtMgBr. Additionally, the use of stoichiometric amounts of magnesium with respect to the phenol is a disadvantage.
Hence, there is still a need to provide a process for the preparation of tris(2-hydroxyphenyl)methane derivatives via a short route with good overall yield under environmentally acceptable conditions, i.e. by avoiding large amounts of potentially toxic organic solvents.